The precise spatial and temporal control of gene expression determines the orderly growth and development of multicellular organisms. Derangement of the ordered pattern of gene expression is associated with abnormal cellular proliferation, oncogenic transformation, and developmental abnormalities. Regulation of gene transcription in response to hormonal and developmental signaling requires the participation of an enormously complicated assortment of nuclear proteins with a diversity of enzymatic and structural functions, including coactivator and corepressor proteins with chromatin remodeling activities. The long-term goals of this project are to understand the physiological roles of transcriptional coregulatory proteins in cellular proliferation and differentiation. The overall goal of experiments outlined in this application is to understand the biochemical mechanism of transcriptional repression mediated by carboxyl-terminal Binding Protein (CtBP), a protein initially identified as a cellular target of the human adenoviral E1A oncoprotein. CtBP and its orthologs are thought to function as corepressors, mediating the activities of a number of cellular sequence-specific DNA-binding proteins that function as transcriptional repressors. CtBP shares biochemical characteristics and structural homology with the 2-hydroxyacid dehydrogenase enzymes. CtBP may therefore act as a sensor of cellular energy balance, raising the possibility that cellular and metabolic stress modulates gene expression through this class of transcriptional coregulatory molecules. In this application we propose to determine how this corepressor mediates the transcriptional repression of cAMP-dependent transcription by E1A, determine what role NAD-binding plays in the corepressor activity of CtBP, and determine the x-ray crystal structure of CtBP.